Refactor: Web Consolidation and Identity Stabilization (#40)

## Overview
This PR completes the architectural consolidation of the web project and stabilizes the Identity-based authentication flow for the NexusReader application. It also refines the UI aesthetic for the Book Ingestion Modal as requested in #33.

## Key Changes
- **Project Consolidation**: Fully merged `NexusReader.Web.New` into `NexusReader.Web`. This includes updating all namespace references, VS Code launch/task configurations, and CI/CD (`Dockerfile`).
- **Identity Stabilization**:
  - Implemented `IIdentityService` on the server using `SignInManager<NexusUser>` and `UserManager<NexusUser>`.
  - Fixed registration logic to include mandatory fields (`SubscriptionPlanId`, `TenantId`).
  - Updated `Login.razor` to force a page reload on successful login, ensuring proper synchronization of authentication cookies between SignalR and the browser.
- **UI/UX Refinement**:
  - Updated `BookIngestionModal` styling to follow the **Nexus Neon** design system.
  - Added premium button styles with hover effects and glows.
  - Improved modal layout and interaction feedback (shimmer effects, spinner colors).
- **Cleanup**: Removed obsolete interfaces and constants that were superseded by newer Application layer implementations.

## Verification
- Successfully built the solution: `dotnet build NexusReader.slnx --no-restore`
- Verified project structure and file moves.
- Validated server-side authentication logic.

Fixes #33

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #40
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.Web/Services/ServerIdentityService.cs

@@ -0,0 +1,121 @@
+using System.Security.Claims;
+using FluentResults;
+using Microsoft.AspNetCore.Identity;
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Application.DTOs.User;
+using NexusReader.Data.Persistence;
+using NexusReader.Domain.Entities;
+using NexusReader.Application.Queries.User;
+using MediatR;
+using NexusReader.Application.Constants;
+using NexusReader.Application.Abstractions.Services;
+
+namespace NexusReader.Web.Services;
+
+public class ServerIdentityService : IIdentityService
+{
+    private readonly UserManager<NexusUser> _userManager;
+    private readonly SignInManager<NexusUser> _signInManager;
+    private readonly IHttpContextAccessor _httpContextAccessor;
+    private readonly IMediator _mediator;
+    private readonly INativeStorageService _storageService;
+
+    public event Func<Task>? OnStateInvalidated;
+
+    public ServerIdentityService(
+        UserManager<NexusUser> userManager,
+        SignInManager<NexusUser> signInManager,
+        IHttpContextAccessor httpContextAccessor,
+        IMediator mediator,
+        INativeStorageService storageService)
+    {
+        _userManager = userManager;
+        _signInManager = signInManager;
+        _httpContextAccessor = httpContextAccessor;
+        _mediator = mediator;
+        _storageService = storageService;
+    }
+
+    public async Task<Result> LoginAsync(string email, string password, bool rememberMe = false) 
+    {
+        try
+        {
+            var user = await _userManager.FindByEmailAsync(email);
+            if (user == null) return Result.Fail("Nieprawidłowy e-mail lub hasło.");
+
+            // Check if account is locked
+            if (await _userManager.IsLockedOutAsync(user)) return Result.Fail("Konto zostało zablokowane.");
+
+            // Check password
+            var isCorrect = await _userManager.CheckPasswordAsync(user, password);
+            if (!isCorrect)
+            {
+                await _userManager.AccessFailedAsync(user);
+                return Result.Fail("Nieprawidłowy e-mail lub hasło.");
+            }
+
+            // Reset access failed count on success
+            await _userManager.ResetAccessFailedCountAsync(user);
+
+            // In Blazor Interactive Server, we cannot use PasswordSignInAsync directly 
+            // because headers are read-only once the circuit is established.
+            // We return success here to indicate credentials are valid.
+            // The UI will then perform a POST redirect to /account/login-form to set cookies.
+            return Result.Ok();
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error($"Błąd podczas weryfikacji poświadczeń: {ex.Message}").CausedBy(ex));
+        }
+    }
+
+    public async Task<Result> LogoutAsync()
+    {
+        // Logout via SignalR is also problematic for cookie clearing.
+        // The UI should redirect to /account/logout-form
+        return Result.Ok();
+    }
+
+    public async Task<Result> RegisterAsync(string email, string password) 
+    {
+        try
+        {
+            var user = new NexusUser 
+            { 
+                UserName = email, 
+                Email = email,
+                SubscriptionPlanId = SubscriptionPlan.FreeId,
+                TenantId = "global"
+            };
+            var result = await _userManager.CreateAsync(user, password);
+            
+            if (result.Succeeded)
+            {
+                // Similar to Login, we return success but don't sign in here.
+                return Result.Ok();
+            }
+            
+            return Result.Fail(result.Errors.Select(e => e.Description).FirstOrDefault() ?? "Rejestracja nie powiodła się.");
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error($"Błąd podczas rejestracji na serwerze: {ex.Message}").CausedBy(ex));
+        }
+    }
+
+    public Task<Result> RefreshTokenAsync() => Task.FromResult(Result.Ok());
+
+    public async Task<Result<UserProfileDto>> GetProfileAsync()
+    {
+        var user = _httpContextAccessor.HttpContext?.User;
+        if (user == null || !user.Identity?.IsAuthenticated == true) return Result.Fail("Not authenticated.");
+
+        var userId = user.FindFirstValue(ClaimTypes.NameIdentifier);
+        if (userId == null) return Result.Fail("User ID not found.");
+
+        var result = await _mediator.Send(new GetUserProfileQuery(userId));
+        if (result.IsFailed) return Result.Fail(result.Errors);
+
+        return Result.Ok(result.Value);
+    }
+}